﻿
namespace TFSChangeLog.ViewModel
{
    using System;
    using System.ComponentModel;
    using System.Diagnostics;

    /// <summary>
    /// Base class for all ViewModel classes in the application.
    /// It provides support for property change notifications 
    /// and has a DisplayName property.  This class is abstract.
    /// </summary>
    public abstract class ViewModelBase : INotifyPropertyChanged, INotifyPropertyChanging, IDisposable
    {
        #region Constructor

        /// <summary>Initializes a new instance of the <see cref="ViewModelBase"/> class.</summary>
        protected ViewModelBase()
        {
        }
        #endregion // Constructor

        #region DisplayName

        /// <summary>Gets or sets (TODO: Fix the documentation here) :: Returns the user-friendly name of this object.
        /// Child classes can set this property to a new value,
        /// or override it to determine the value on-demand.</summary>
        public virtual string DisplayName { get; protected set; }

        #endregion // DisplayName

        #region Debugging Aides

        /// <summary>
        /// Warns the developer if this object does not have
        /// a public property with the specified name. This 
        /// method does not exist in a Release build.
        /// </summary>
        /// <param name="propertyName">TODO: Summary description for <c>propertyName</c> parameter of type <c>string</c>.</param>
        [Conditional("DEBUG")]
        [DebuggerStepThrough]
        public void VerifyPropertyName(string propertyName)
        {
            // Verify that the property name matches a real,  
            // public, instance property on this object.
            if (TypeDescriptor.GetProperties(this)[propertyName] == null)
            {
                string msg = "Invalid property name: " + propertyName;

                if (this.ThrowOnInvalidPropertyName)
                    {
                    throw new Exception(msg);
                    }
                else
                    Debug.Fail(msg);
            }
        }

        /// <summary>Gets a value indicating whether (TODO: Fix the documentation here) :: Returns whether an exception is thrown, or if a Debug.Fail() is used
        /// when an invalid property name is passed to the VerifyPropertyName method.
        /// The default value is false, but subclasses used by unit tests might 
        /// override this property's getter to return true.</summary>
        protected virtual bool ThrowOnInvalidPropertyName { get; private set; }

        #endregion // Debugging Aides

        #region INotifyPropertyChanged Members

        /// <summary>
        /// Raised when a property on this object has a new value.
        /// </summary>
        public event PropertyChangedEventHandler PropertyChanged;

        /// <summary>
        /// Raises this object's PropertyChanged event.
        /// </summary>
        /// <param name="propertyName">The property that has a new value.</param>
        protected internal virtual void OnPropertyChanged(string propertyName)
        {
            this.VerifyPropertyName(propertyName);

            PropertyChangedEventHandler handler = this.PropertyChanged;
            if (handler != null)
            {
                var e = new PropertyChangedEventArgs(propertyName);
                handler(this, e);
            }
        }

        #endregion // INotifyPropertyChanged Members

        #region INotifyPropertyChanging Members

        /// <summary>Summary description for <c>PropertyChanging</c> event.</summary>
        public event PropertyChangingEventHandler PropertyChanging;

        /// <summary>
        /// Raises this object's PropertyChanging event.
        /// </summary>
        /// <param name="propertyName">The property that has a new value.</param>
        protected virtual void OnPropertyChanging(string propertyName)
        {
            this.VerifyPropertyName(propertyName);

            PropertyChangingEventHandler handler = this.PropertyChanging;
            if (handler != null)
            {
                var e = new PropertyChangingEventArgs(propertyName);
                handler(this, e);
            }
        }

        #endregion

        #region IDisposable Members

        /// <summary>
        /// Invoked when this object is being removed from the application
        /// and will be subject to garbage collection.
        /// </summary>
        public void Dispose()
        {
            this.OnDispose();
        }

        /// <summary>
        /// Child classes can override this method to perform 
        /// clean-up logic, such as removing event handlers.
        /// </summary>
        protected virtual void OnDispose()
        {
        }

#if DEBUG
        /// <summary>Finalizes an instance of the <see cref="ViewModelBase"/> class.
        /// Useful for ensuring that ViewModel objects are properly garbage collected.</summary>
        ~ViewModelBase()
        {
            string msg = string.Format("{0} ({1}) ({2}) Finalized", this.GetType().Name, this.DisplayName, this.GetHashCode());
            System.Diagnostics.Debug.WriteLine(msg);
        }
#endif

        #endregion // IDisposable Members
    }
}